Doctor of Philosophy, The Ohio State University, 2023, Materials Science and Engineering

This thesis reports experimental data on the transport properties of ferroelectric and ferromagnetic solids, as well as topological insulators. The analogies between the thermal perturbations of ferroelectric and ferromagnetic order are explored from a fundamental point of view. While ferromagnetic order is the object of an established field of study, spin caloritronics, the study of perturbations in ferroelectrics stands to establish a new field, polarization caloritronics. This new field, following in the footsteps of its predecessor, has the potential to impact thermoelectricity, heat controlling devices and possibly phonon-based logic. The first subject of this dissertation is a new quasiparticle, the ferron, defined as the elementary thermal excitation of polarization in a ferroelectric material. Likening the ferron to the quantum of a spin wave, the magnon, we measured the ferronic thermal conductivity in lead zirconium titanate (PZT), a well-established ferroelectric material. With the assistance of resonant ultrasound spectroscopy (RUS) to establish the electric field dependent sound velocity, we determined that optical phonons hybridize with acoustic phonons assisting in the formation of a polarization-lattice coupled phonon, coined the ferron. The ferron theory states that the electric field dependent sound velocity and thermal conductivity can be predicted with three material properties: the Gruneisen parameter which quantifies the anharmonicity of the phonon dispersion with respect to volume changes, and d33 and d31, which are the piezoelectric coefficients which quantify the parallel and perpendicular strain of the system in an electric field, respectively. The predicted field dependency using published values for PZT agreed well with our observations. To further test this theory, we performed RUS and thermal conductivity measurements on a relaxor ferroelectric, a solid solution of lead magnesium niobate and lead titanate (PMN-PT). Here, the theory (open full item for complete abstract)

Committee: Joseph Heremans (Advisor); Wolfgang Windl (Committee Member); Roberto Myers (Committee Member); Patrick Taylor (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2020, Mechanical Engineering

Thermal management is critical for both nuclear and electronics industry because of heat generation during the operation. Major part of energy consumed in microelectronic devices and nuclear reactors dissipates as heat, and sometimes also creates hot spots. This is critical and precarious for the nuclear applications, while for the electronics, it has detrimental effects on the device performance and affects the reliability of devices. The microelectronic devices and nuclear materials are exposed to the extreme environments such as irradiation, vacuum, and molten salts etc. In addition to the already existing intrinsic defects, this exposure leads to the creation of multiple defects inside the materials. The goal of this research is to understand the phonon transport physics at these small length scales due to intrinsic and extrinsic defects in the material. Primarily, three different materials are discussed in this report. SiC and sapphire have been chosen for their applications in both microelectronic devices and nuclear industry while ceria has been studied as a surrogate material for the nuclear fuels (UO2 and ThO2). There are different kinds of defects created inside the material when exposed to irradiation. The complex interaction of phonons with these defects dictates the resultant thermal transport however, it is difficult to apportion the impact of a particular type of defect. The approach used here employs materials induced with only a few types of defects at a time in order to isolate and study the impact of induced defect on thermal transport. Consequently, irradiation has been used in this study to induce desired defects inside the material and thereafter study their effect on thermal conductivity. Interstitials and vacancies, collectively known as point defects are formed under low dose and heavy ion irradiation regime. Here, SiC is irradiated using Kr ions to study impact of point defects on its vibrational and thermal properties. While th (open full item for complete abstract)

Committee: Marat Khafizov Prof. (Advisor); Igor Adamovich Prof. (Committee Member); Sandip Mazumder Prof. (Committee Member); David Hurley Dr. (Committee Member) Subjects: Condensed Matter Physics; Materials Science; Mechanical Engineering; Nanoscience; Nuclear Engineering; Nuclear Physics

Master of Science, Miami University, 2021, Mechanical and Manufacturing Engineering

Programmed self-assembly provides a promising platform toward the design of functional metamaterials through tunable surface interactions of colloidal particles. Recent studies demonstrated experimental fabrication of novel microstructures through spontaneous solution-based self-assembly. These processes enable the desirable placement of a wide variety of building blocks into nanoengineered structures with tunable material and transport properties. The vast majority of self-assembled structures presented in concurrent literature are historically limited to basic or binary classifications consisting of only one or two types of distinctly interacting building blocks. Recent developments in linker-mediated assembly processes allow for interactions to be coordinated between many different types of colloidal particles more easily and with fewer unique sequences than direct hybridization. However, the dynamics of programmed self-assembly becomes increasingly more complex when coordinating interactions between three or more distinct interacting elements. In such cases particle pairs with similar binding energy are allowed to interact unpredictably, and enthalpically degenerate binding sites will be noticeably more present while numerous secondary phases may also result from the self-assembly process. Therefore, it is necessary to develop procedures for predicting feasible superstructure geometries for these systems before they can be implemented in material design. This thesis presents molecular dynamics simulations and thermodynamic free energy calculations of self-assembled colloidal structures. These results provide direct guidelines for designing multifarious colloidal structures from three or more types of building blocks and motivate new directions for future experimental work to target formation of multi-component colloidal superstructures beyond the well-established binary symmetries studied in the past. Phononic and thermal transport properties of self-assem (open full item for complete abstract)

Committee: Mehdi Zanjani (Advisor); Andrew Paluch (Committee Member); Carter Hamilton (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2017, Materials Science and Engineering

Complex interactions between spin, charge, and heat currents have set the stage for some of the most exciting physics experiments of the early 21st century. The desire to understand these interactions has inspired physicists, engineers, and material scientists, particularly in the fields of spin caloritronics and magnonics, both of which are focused on answering questions involving spin and heat interactions and the transport of pure spin current. To provide a means for understanding both the physical phenomena and technological applications associated with spin transport, the opto-thermal measurement has been developed. This experimental technique serves as a way to probe the generation, transport, and detection of spin currents by utilizing the spin Seebeck effect (SSE). The measurement involves using a laser to induce a highly localized thermal gradient, which results in the generation of a spin current in a magnetic insulator (FM). This spin current is then detected in an adjacent normal metal (NM) via the inverse spin Hall effect. The opto-thermal technique is used to study the generation of spin current in the presence of photo excited charge carriers and also to study the SSE on an ultrafast time scale. It is demonstrated that the opto-thermal technique is highly efficient for studying the myriad of different FM/NM systems relevant to the SSE. The nonlocal opto-thermal measurement is used to study the spin diffusion length in Yttrium Iron Garnet (YIG).

Committee: Roberto Myers (Advisor); Joseph Heremans (Committee Member); Wolfgang Windl (Committee Member) Subjects: Materials Science

Master of Science in Renewable and Clean Energy Engineering (MSRCE), Wright State University, 2016, Renewable and Clean Energy

Nanomaterials hold great promise for applications in thermal management and thermoelectric power generation. Defects in these are important as they are generally inevitably introduced during fabrication or intentionally engineered to control the properties of the nanomaterials. Here, we investigate how phonon-contributed thermal conductance in narrow graphene, boron nitride (BN), and silicene nanoribbons (NRs), responds to the presence of a vacancy defect and the corresponding geometric distortion, from first principles using the non-equilibrium Green's function method. Analyses are made of the geometries, phonon conductance coefficients, and local densities of states (LDOS) of pristine and defected nanoribbons. It is found that hydrogen absences produce similar reductions in thermal conductance in planar graphene and BN NRs with greater reductions in buckled silicene NRs. Vacancies of larger atoms affect all systems similarly, causing greater reductions than hydrogen absences. Emerging flexible and stiff scattering centers, depending on bond strengths, are shown to cause thermal conductance reduction by changing nearby LDOSs in defected structures relative to pristine ones. This knowledge suggests that inferences on unknown thermal properties of novel defected materials can be made based on understanding how thermal transport behaves in their analogues and how bond characteristics differ between systems under consideration. The thermal conductance contributed by phonons is often a limiting factor to the overall suitability of a material for use in thermoelectric power generation, wherein a voltage is generated in a material by a temperature gradient. The thermoelectric figure of merit (ZT) assesses this suitability, in part based on a ratio of electrical conductance to thermal conductance. These two properties can be decoupled in low-dimensional structures like NRs, with lower thermal conductances generally found in narrower materials. Here, ZT is analyzed in g (open full item for complete abstract)

Committee: Amir Farajian Ph.D. (Advisor); Hong Huang Ph.D. (Committee Member); James Menart Ph.D. (Committee Member) Subjects: Energy; Engineering; Materials Science; Nanotechnology; Solid State Physics

Doctor of Philosophy (PhD), Wright State University, 2014, Engineering PhD

Novel silicene-based nanomaterials are designed and characterized by first principle computer simulations to assess the effects of adsorptions and defects on stability, electronic, and thermal properties. To explore quantum thermal transport in nanostructures a general purpose code based on Green's function formalism is developed. Specifically, we explore the energetics, temperature dependent dynamics, phonon frequencies, and electronic structure associated with lithium chemisorption on silicene. Our results predict the stability of completely lithiated silicene sheets (silicel) in which lithium atoms adsorb on the atom-down sites on both sides of the silicene sheet. Upon complete lithiation, the band structure of silicene is transformed from a zero-gap semiconductor to a 0.368 eV bandgap semiconductor. This new, uniquely stable, two-atom-thick, semiconductor material could be of interest for nanoscale electronic devices. We further explore the electronic tunability of silicene through molecular adsorption of CO, CO2, O2, N2, and H2O on nanoribbons for potential gas sensor applications. We find that quantum conduction is detectibly modified by weak chemisorption of a single CO molecule on a pristine silicene nanoribbon. Moderate binding energies provide an optimal mix of high detectability and recoverability. With Ag contacts attached to a ~ 1 nm silicene nanoribbon, the interface states mask the conductance modulations caused by CO adsorption, emphasizing length effects for sensor applications. The effects of atmospheric gases: nitrogen, oxygen, carbon dioxide, and water, as well as CO adsorption density and edge-dangling bond defects, on sensor functionality are also investigated. Our results reveal pristine silicene nanoribbons as a promising new sensing material with single molecule resolution. Next, the thermal conductance of silicene nanoribbons with and without defects is explored by Non-Equilibrium Green's function method as implemented in our Th (open full item for complete abstract)

Committee: Amir Farajian Ph.D. (Advisor); Khalid Lafdi Ph.D. (Committee Member); Sharmila Mukhopadhyay Ph.D. (Committee Member); Ajit Roy Ph.D. (Committee Member); H. Daniel Young Ph.D. (Committee Member) Subjects: Materials Science; Nanoscience; Nanotechnology

Doctor of Philosophy, Case Western Reserve University, 2014, EMC - Mechanical Engineering

The total thermal resistance of a thermal interface material (TIM) depends on its thermal conductivity, bond line thickness (BLT) and the contact resistances of the TIM with the two bounding surfaces. This work reports development and thermal characterization of tin-capped vertically aligned multi-walled carbon nanotube (VA-MWCNT) array-epoxy composites for thermal energy management in load-bearing structural applications. The epoxy matrix is expected to impart mechanical strength to these systems while the VA-MWCNTs provide avenues for high thru-thickness thermal conductivity across the material interface. A transition zone (capping layer) comprising of a Sn thin film is introduced at the interface between the MWCNTs and the bounding surfaces to minimize the total interface thermal resistance of the TIM. Three-omega measurement method is utilized to characterize thermal conductivity in the tin-capped VA-MWCNT-epoxy composites as well as in its individual constituents, i.e. bulk EPON-862 (matrix) from 40K-320K, tin thin films in the temperature range 240K-300K and in individual MWCNTs at room temperature, taken from the same VA-MWCNT batch as the one used to fabricate the CNT-epoxy composites. Multilayer thermal model that includes effects of thermal interface resistance is developed to interpret the experimental results. The thermal conductivity of the carbon nanotube-epoxy composite is estimated to be ~ 5.8 W/m-K, and exhibits a slight increase in the temperature range of 240 K to 300 K. The results of the study suggests that the morphological structure/quality of the individual MWCNTs as well as the tin thin layer on the VA-MWCNT array are dominating factors that control the overall thermal conductivity of the TIM. These results are encouraging in light of the fact that the thermal conductivity of a VA-MWCNT array can be increased by an order of magnitude by using a standard high temperature post-annealing step. In this way, multifunctional (load bearing) T (open full item for complete abstract)

Committee: Vikas Prakash (Committee Chair); Yasuhiro Kamotani (Committee Member); Jaikrishnan Kadambi (Committee Member); Xiong Yu (Committee Member) Subjects: Condensed Matter Physics; Mechanical Engineering; Nanoscience; Nanotechnology

Master of Science, The Ohio State University, 2009, Mechanical Engineering

Heat conduction in crystalline semiconductor materials occurs by lattice vibrations that result in the propagation of quanta of energy called phonons. The Boltzmann Transport Equation (BTE) for phonons is a powerful tool to model both equilibrium and non-equilibrium heat conduction in crystalline solids. Non-equilibrium heat conduction occurs either when the length scales (of the device in question) are small or at low temperatures. The BTE describes the evolution of the number density (or energy) distribution for phonons as a result of transport (or drift) and inter-phonon collisions. The Monte-Carlo (MC) method has found prolific use in the solution of the Boltzmann Transport Equation (BTE) for phonons. This thesis contributes to the state-of-the-art by performing a systematic study of the role of the various phonon modes on thermal conductivity predictions-in particular, optical phonons. A procedure to calculate three-phonon scattering time-scales with the inclusion of optical phonons is described and implemented. The roles of various phonon modes are assessed. It is found that Transverse Acoustic (TA) phonons are the primary carriers of energy at low temperatures. At high temperatures (T > 200 K), Longitudinal Acoustic (LA) phonons carry more energy than TA phonons. When optical phonons are included, there is a significant change in the amount of energy carried by various phonons modes, especially at room temperature, where optical modes are found to carry about 25% of the energy at steady state in silicon thin films. Most importantly, it is found that inclusion of optical phonons results in better match with experimental observations for silicon thin-film thermal conductivity. The inclusion of optical phonons is found to decrease the thermal conductivity at intermediate temperatures (50-200 K) and increase it at high temperature (>200 K), especially when the film is thin. The effect of number of stochastic samples, the dimensionality of the computational domain (open full item for complete abstract)

Committee: Sandip Mazumder PhD (Advisor); Vishwanath Subramaniam PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy (PhD), Ohio University, 2010, Physics and Astronomy (Arts and Sciences)

In this dissertation, four topics related to the physics and astrophysics of neutron stars are studied. Two first topics deal with microscopical physics processes in the star outer crust and the last two with macroscopical properties of a star, such as mass and radius. In the first topic, the thermodynamical and transport properties of a dilute gas in which particles interact through a delta-shell potential are investigated. Through variations of a single parameter related to the strength and size of the delta-shell potential, the scattering length and effective range that determine the low-energy elastic scattering cross sections can be varied over wide ranges including the case of the unitary limit (infinite scattering length). It is found that the coefficients of shear viscosity, thermal conductivity and diffusion all decrease when the scattering length becomes very large and also when resonances occur as the temperature is increased. The calculated ratios of the shear viscosity to entropy density as a function of temperature for various interaction strengths (and therefore scattering lengths) were found to lie well above the recently suggested minimal value of (4π)-1 ℏ/kB. A new result is the value of (4/5) for the dimensionless ratio of the energy density times the diffusion coefficient to viscosity for a dilute gas in the unitary limit. Whether or not this ratio changes upon the inclusion of more than two-body interactions is an interesting avenue for future investigations. These investigations shed pedagogical light on the issue of the thermal and transport properties of an interacting system in the unitary limit, of much current interest in both atomic physics and nuclear physics in which very long scattering lengths feature prominently at very low energies. In the second topic, the shear viscosity of a Yukawa liquid, a model for the outer crust of a neutron star, is calculated in both the classical and quantum regimes. Results of semi-analytic calculations (open full item for complete abstract)

Committee: Madappa Prakash Prof. (Advisor); Markus Bottcher Prof. (Committee Member); Daniel Phillips Prof. (Committee Member); David Drabold Prof. (Committee Member); Klaus Himmeldirk Prof. (Committee Member) Subjects: Astronomy; Astrophysics; Nuclear Physics; Particle Physics; Physics

Doctor of Philosophy, Case Western Reserve University, 2005, Mechanical Engineering

A Numerical Study of Transport Phenomena in Porous Media Abstract by May-Fun Liou Since Darcy's pioneering experimental study of porous medium flow, a great number of analytical, numerical, and experimental works have been carried out to provide qualitatively and quantitatively macroscopic descriptions of the overall viscous resistance or heat transfer across the porous media. Recent advances in experimental measuring techniques have uncovered the importance of structural heterogeneity within the porous media. Thus, in order to gain a better understanding of phenomena at the scale of pores, new numerical approaches must be taken. A general numerical simulation capability at pore-scale level is developed and validated in this thesis study, predicting global phenomena in close agreement with classical results. This technique has been successfully applied to two and three dimensional porous systems. In particular, it is shown that three dimensional solutions that couples the fluid and solid systems simultaneously at the pore scale are feasible with today's computer resources and are extremely beneficial, shedding a new light into phenomena unavailable otherwise. This study also emphasizes numerical simulations of mass, momentum, and heat transfer phenomena induced in complex porous media, providing details of local velocity profiles and heat transfer. It is shown that the porous structures – shape, size, and locations have significant effects on the macroscopic description. It is concluded that a microscopic description at the pore scale should be included in the study of porous medium flow. The flow pathlines are tortuous, determined by the local pore structure. Hence, the mixing caused by a porous insert can offer an efficient way to dissipate the heat from the heat source. The qualitative description of transport phenomena of flow through a three-dimensional duct demonstrates the capability of the numerical approach proposed in this thesis. It is also found that the (open full item for complete abstract)

Committee: Isaac Greber (Advisor) Subjects: